Outside the bar the argument turned physical, and when Uthai tried to intervene the couple attacked him, officials said.

The police officer told investigators that Del Pinto had tried to grab his pistol and the gun "accidentally went off" three times.

"The policeman, who is about 1.6m tall, was beaten to the ground by the man, a bodybuilder, and the hippy woman," said the local police chief, Wanchai Suwanririkate.

Del Pinto, a frequent visitor to Pai, died at the scene, while Reisig was rushed to hospital in the nearby province of Chiang Mai. One of the bullets grazed her upper left torso but her foetus was unharmed, Sombat said.

Uthai was charged with premeditated murder for Del Pinto's death, and with "intent to kill" in connection with Reisig, Sombat added.

A spokesman for the Canadian embassy in Bangkok was not available for comment. It is not known where in Canada the couple were from.